1. Field of the Invention
The present invention relates primarily to a ceiling-suspended support apparatus for medical appliances supported so as to be movable vertically, such as an operation microscope, X-ray equipment, laser scalpel or the like, and more particularly to an improvement in the fall-prevention mechanism thereof.
2. Description of the Prior Art
Well known ceiling-suspended support apparatuses for medical appliances are arranged such that a pulley is rotatably supported above a lifter adapted to hold a medical appliance at the lower end thereof, and move vertically in a support casing, and the lifter and a counterweight are held at opposite ends of a wire passed over the pulley so as to balance the weight of each other. Various types of fall-prevention mechanism have been proposed for preventing the fall of the lifter when the tension in the wire of this type of support apparatus is reduced by the wire breaking or coming off the pulley. For example, Japanese Utility Model Publication No. 5253/1974 disclosed a fall-prevention mechanism for the support apparatus. The mechanism is arranged such that a wedge which is pulled toward a lifter by means of a spring is normally pulled by a wire connected to a counterweight in the direction opposite to the direction of pull of the spring against the force thereof, so that when the wire breaks, the wedge is pulled by means of the tensile force of the spring so as to press against a slide pin, which brings a braking member into pressure-contact with a support wall, thereby preventing the fall of the lifter by means of the frictional force of the braking member.
In such a conventional supporting apparatus for a medical appliance, however, the slide pin pressing the fall-prevention braking member against the support wall has a fixed direction of movement which is perpendicular to the axial direction of the support, and also the direction of the compression force of the braking member is perpendicular to the axial direction of the support. Therefore, a much larger compression force is required in order to prevent the lifter falling. Since the spring means pulling the wedge must also have a large tension in proportion to the compression force, it is also necessary to increase the size of the counterweight to balance its weight with that of the lifter against the force of the spring means, resulting in an undesirable increase in the size of the support itself, solely to suspend the counterweight. Moreover, in order to increase the frictional force of the braking means, it is necessay to increase the contact area thereof, and this brings about an increase in the size in the fall-prevention mechanism itself, and the support apparatus is larger in size as a whole, resulting in a higher cost. In addition, a wider installation area is required, so that the operating room, etc., where such a support apparatus is installed is more cramped, which could be inconvenient to the surgeon or other operator of the support apparatus.
Moreover, since a conventional support apparatus for a medical appliance has no means for preventing the counterweight falling, a fall of the counterweight may destroy the electrical circuits, etc., inside the stand.